z3fold: fix potential race in z3fold_reclaim_page
It is possible that on a (partially) unsuccessful page reclaim,
kref_put() called in z3fold_reclaim_page() does not yield page release,
but the page is released shortly afterwards by another thread. Then
z3fold_reclaim_page() would try to list_add() that (released) page again
which is obviously a bug.
To avoid that, spin_lock() has to be taken earlier, before the
kref_put() call mentioned earlier.
Link: http://lkml.kernel.org/r/20170913162937.bfff21c7d12b12a5f47639fd@gmail.com
Signed-off-by: Vitaly Wool <vitalywool@gmail.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: <Oleksiy.Avramchenko@sony.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/z3fold.c b/mm/z3fold.c
index 486550d..b04fa3b 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -875,16 +875,18 @@
goto next;
}
next:
+ spin_lock(&pool->lock);
if (test_bit(PAGE_HEADLESS, &page->private)) {
if (ret == 0) {
+ spin_unlock(&pool->lock);
free_z3fold_page(page);
return 0;
}
} else if (kref_put(&zhdr->refcount, release_z3fold_page)) {
atomic64_dec(&pool->pages_nr);
+ spin_unlock(&pool->lock);
return 0;
}
- spin_lock(&pool->lock);
/*
* Add to the beginning of LRU.